Pharmacokinetics of haloperidol in psychotic patients

Development and Evaluation of a Physiologically Based Pharmacokinetic Model for Predicting Haloperidol Exposure in Healthy and Disease Populations

The physiologically based pharmacokinetic (PBPK) approach can be used to develop mathematical models for predicting the absorption, distribution, metabolism, and elimination (ADME) of administered drugs in virtual human populations. Haloperidol is a typical antipsychotic drug with a narrow therapeutic index and is commonly used in the management of several medical conditions, including psychotic disorders. Due to the large interindividual variability among patients taking haloperidol, it is very likely for them to experience either toxic or subtherapeutic effects. We intend to develop a haloperidol PBPK model for identifying the potential sources of pharmacokinetic (PK) variability after intravenous and oral administration by using the population-based simulator, PK-Sim. The model was initially developed and evaluated to predict the PK of haloperidol and its reduced metabolite in adult healthy population after intravenous and oral administration. After evaluating the developed PBPK model in healthy adults, it was used to predict haloperidol–rifampicin drug–drug interaction and was extended to tuberculosis patients. The model evaluation was performed using visual assessments, prediction error, and mean fold error of the ratio of the observed-to-predicted values of the PK parameters. The predicted PK values were in good agreement with the corresponding reported values. The effects of the pathophysiological changes and enzyme induction associated with tuberculosis and its treatment, respectively, on haloperidol PK, have been predicted precisely. For all clinical scenarios that were evaluated, the predicted values were within the acceptable two-fold error range.

β-Cyclodextrin-based ternary complexes of haloperidol and organic acids: the effect of organic acids on the drug solubility enhancement

Haloperidol (HALO) is a weak base with very low aqueous solubility that is used as an antipsychotic drug. This study aimed to improve its solubility by forming HALO/β-cyclodextrin (β-CD)-based ternary complexes with organic acids. The solubility of HALO/β-CD binary and HALO/β-CD/organic acid ternary complexes in different media (i.e. citrate buffer pH 3 and 6) was explored. The stoichiometric ratio between the drug and β-CD was 1:1 in all complexes formed. The solubility of HALO/β-CD binary complexes significantly increased in citrate buffer pH 3 compared with citrate buffer pH 6. For the ternary complexes, HALO/β-CD/tartaric acid and HALO/β-CD/lactic acid in citrate buffer pH 3 increased HALO solubility compared with HALO/β-CD/succinic acid due to their higher unionized species. The highest stability constant and complexation efficiency values in citrate buffer pH 3 were shown by the ternary complexes with lactic acid followed by tartaric acid and succinic acid, respectively. Results indicated that lactic acid provided the greatest binding strength and solubilization efficiency for the complex.

Population pharmacokinetics of haloperidol in terminally ill adult patients

Purpose

Over 80% of the terminally ill patients experience delirium in their final days. In the treatment of delirium, haloperidol is the drug of choice. Very little is known about the pharmacokinetics of haloperidol in this patient population. We therefore designed a population pharmacokinetic study to gain more insight into the pharmacokinetics of haloperidol in terminally ill patients and to find clinically relevant covariates that may be used in developing an individualised dosing regimen.

Methods

Using non-linear mixed effects modelling (NONMEM 7.2), a population pharmacokinetic analysis was conducted with 87 samples from 28 terminally ill patients who received haloperidol either orally or subcutaneously. The covariates analysed were patient and disease characteristics as well as co-medication.

Results

The data were accurately described by a one-compartment model. The population mean estimates for oral bioavailability, clearance and volume of distribution for an average patient were 0.86 (IIV 55%), 29.3 L/h (IIV 43%) and 1260 L (IIV 70%), respectively. This resulted in an average terminal half-life of haloperidol of around 30 h.

Conclusion

Our study showed that the pharmacokinetics of haloperidol could be adequately described by a one-compartment model. The pharmacokinetics in terminally ill patients was comparable to other patients. We were not able to explain the wide variability using covariates.

A physiologically based pharmacokinetic model to predict the pharmacokinetics of highly protein-bound drugs and the impact of errors in plasma protein binding

Predicting the pharmacokinetics of highly protein-bound drugs is difficult. Also, since historical plasma protein binding data were often collected using unbuffered plasma, the resulting inaccurate binding data could contribute to incorrect predictions. This study uses a generic physiologically based pharmacokinetic (PBPK) model to predict human plasma concentration-time profiles for 22 highly protein-bound drugs. Tissue distribution was estimated from in vitro drug lipophilicity data, plasma protein binding and the blood: plasma ratio. Clearance was predicted with a well-stirred liver model. Underestimated hepatic clearance for acidic and neutral compounds was corrected by an empirical scaling factor. Predicted values (pharmacokinetic parameters, plasma concentration-time profile) were compared with observed data to evaluate the model accuracy. Of the 22 drugs, less than a 2-fold error was obtained for the terminal elimination half-life (t1/2 , 100% of drugs), peak plasma concentration (Cmax , 100%), area under the plasma concentration-time curve (AUC0-t , 95.4%), clearance (CLh , 95.4%), mean residence time (MRT, 95.4%) and steady state volume (Vss , 90.9%). The impact of fup errors on CLh and Vss prediction was evaluated. Errors in fup resulted in proportional errors in clearance prediction for low-clearance compounds, and in Vss prediction for high-volume neutral drugs. For high-volume basic drugs, errors in fup did not propagate to errors in Vss prediction. This is due to the cancellation of errors in the calculations for tissue partitioning of basic drugs. Overall, plasma profiles were well simulated with the present PBPK model. Copyright © 2016 John Wiley & Sons, Ltd.

Dopaminergic receptor blockade changes a functional connectivity network centred on the amygdala

Resting-state connectivity has become an increasingly important measure in characterizing the functional integrity of brain circuits in neuro-psychiatric conditions. One approach that has recently gained prominence in this regard-and which we use in this study-is to investigate how resting-state connectivity depends on the integrity of certain neuromodulator systems. Here, we use a pharmacological challenge in combination with functional magnetic resonance imaging to investigate the impact of dopaminergic receptor blockade on whole brain functional connectivity in twenty healthy human subjects. Administration of the D2-receptor antagonist haloperidol led to a profound change in functional integration in network nodes linked to the amygdala. Compared to placebo and baseline measurements, network-based statistics and pairwise connectivity analyses revealed reduced connectivity and decreased link strength between the amygdala and the bilateral posterior cingulate cortex and other cortical areas. This was complemented by less extensive but very circumscribed enhanced connectivity between the amygdala and the right putamen during D2-receptor blockade. It will be interesting to investigate whether these pharmacologically induced shifts in resting-state connectivity will similarly be evident in clinical conditions that involve a dysfunction of the dopaminergic system. Our findings might also aid in interpreting alterations in more complex states, such as those seen psychiatric conditions and their treatment. Hum Brain Mapp 37:4148-4157, 2016. © 2016 Wiley Periodicals, Inc.

Haloperidol dose combined with dexamethasone for PONV prophylaxis in high-risk patients undergoing gynecological laparoscopic surgery: a prospective, randomized, double-blind, dose-response and placebo-controlled study

Background

Low-dose haloperidol is known to be effective for the prevention of postoperative nausea and vomiting (PONV). However, precise dose-response studies have not been completed, especially in patients at high risk for PONV who require combination therapy. This study sought to identify which dose of haloperidol 1mg or 2mg could be combined with dexamethasone without adverse effects in high-risk patients undergoing gynecological laparoscopic surgery.

Methods

Female adults (n = 150) with three established PONV risk factors based on Apfel’s score were randomized into one of three study groups. At the end of anesthesia, groups H0, H1, and H2 were given intravenous (IV) saline, haloperidol 1 mg, and haloperidol 2 mg, respectively. All patients were given dexamethasone 5 mg during the induction of anesthesia. The overall early (0–2 h) and late (2–24 h) incidences of nausea, vomiting, rescue anti-emetic administration, pain, and adverse effects (cardiac arrhythmias and extrapyramidal effects) were assessed postoperatively. The sedation score was recorded in the postanesthesia care unit (PACU).

Results

The total incidence of PONV over 24 h was significantly lower in groups H1 (29 %) and H2 (24 %) than in group H0 (54 %; P = 0.003), but there was no significant difference between groups H1 and H2. In the PACU, group H2 had a higher sedation score than groups H1 and H0 (P < 0.001).

Conclusions

For high-risk PONV patients undergoing gynecological laparoscopic surgery, when used with dexamethasone, 1-mg haloperidol was equally effective as 2 mg in terms of preventing PONV with the less sedative effect.

Trial Registration

ClinicalTrials.gov (NCT01639599).

Intraoperative haloperidol does not improve quality of recovery and postoperative analgesia

Introduction:

Haloperidol has an established role in nausea and vomiting prophylaxis and possible effects on multiple aspects of postoperative recovery including pain and sedation. The purpose of this study was to evaluate the effects of low-dose intraoperative intravenous haloperidol on quality of recovery (QoR) and pain control after general anesthesia and surgery.

Methods:

Ninety eight American Society of Anesthesiologists (ASA) physical status I-II patients undergoing elective general, gynecologic or orthopedic surgery under general anesthesia were enrolled. Participants were randomly allocated to receive either haloperidol 2 mg or sterile water intravenously after induction of anesthesia. All patients were given elastometric morphine patient-controlled analgesia (PCA) pump for pain control after the surgery. Post-operative QoR was evaluated within 20 min in the recovery room and 6 h post-operatively. Pain intensity and demand for additional analgesic was measured in the 6^th post-operative hour.

Results:

The QoR score in two measurements was not statistically different between the two groups. Haloperidol significantly reduced the nausea in the recovery. The visual analog scale pain score showed that the severity of pain in the haloperidol group was more than the placebo group (4.7 ± 2.4 vs. 3.8 ± 2.5, P = 0.05).

Conclusion:

Intraoperative small-dose IV haloperidol is effective against post-operative nausea and vomiting with no significant effect on overall QoR. It may also attenuate the analgesic effects of morphine PCA.

Clinical pharmacology of dopamine-modulating agents in Tourette's syndrome

Forty years of research and clinical practice have proved dopamine (DA) receptor antagonists to be effective agents in the treatment of Tourette's syndrome (TS), allowing a significant tic reduction of about 70%. Their main effect seems to be mediated by the blockade of the striatal DA-D2 receptors. Various typical and atypical agents are available and there is still discord between experts about which of them should be considered as first choice. In addition, there are suggestions to use DA receptor agonists such as pergolide or non-DA-modulating agents. The present chapter is focusing on the clinical pharmacology of DA-modulating agents in the treatment of TS. The introduction outlines their clinical relevance and touches on the hypotheses of the role of DA in the pathophysiology of TS. Subsequently, general information about the mechanisms of action and adverse effects are provided. The central part of the chapter forms a systematic review of all DA-modulating agents used in the treatment of TS, including an overview of studies on their effectiveness, and a critical discussion of their specific adverse effects. The present chapter closes with a summary of the body of evidence and a description of the resulting recommendations for the pharmacological treatment of TS.

Secondary pseudomyopia induced by amisulpride

PURPOSE

To report a case of pseudomyopia induced by antipsychotic drug administration.

METHODS

A 30-year-old woman was referred to our ophthalmology department complaining of blurred vision, especially at distance, in both eyes. The patient had been prescribed antipsychotic drugs (haloperidol and biperiden) as treatment for her schizophrenic symptoms and had recently undergone a change of treatment to amisulpride. She had a manifest refraction of -4.00/-1.00 × 180 in the OD and -3.75/-1.25 × 175 in the OS whereas her cycloplegic refraction was -1.75/-1.00 × 180 in the OD and -1.00/-1.25 × 175 in the OS, respectively.

RESULTS

A diagnosis of likely drug-induced pseudomyopia was made. Therefore, the patient was advised to visit her psychiatrist, who added an extra 2 mg of biperiden, an anticholinergic agent, to the pre-existing amisulpride treatment, achieving a cessation of the visual symptoms a few days later.

CONCLUSIONS

Pseudomyopia can be induced by the antipsychotic drug amisulpride. Additional treatment with anticholinergic agents can be used to eliminate this side effect.

Dopamine D2 occupancy as a biomarker for antipsychotics: quantifying the relationship with efficacy and extrapyramidal symptoms

For currently available antipsychotic drugs, blockade of dopamine D(2) receptors is a critical component for achieving antipsychotic efficacy, but it is also a driving factor in the development of extrapyramidal symptoms (EPS). To inform the clinical development of asenapine, generic mathematical models have been developed for predicting antipsychotic efficacy and EPS tolerability based on D(2) receptor occupancy. Clinical data on pharmacokinetics, D(2) receptor occupancy, efficacy, and EPS for several antipsychotics were collected from the public domain. Asenapine data were obtained from in-house trials. D(2) receptor occupancy data were restricted to published positron emission tomography studies that included blood sampling for pharmacokinetics. Clinical efficacy data were restricted to group mean endpoint data from short-term placebo-controlled trials, whereas EPS evaluation also included some non-placebo-controlled trials. A generally applicable model connecting antipsychotic dose, pharmacokinetics, D(2) receptor occupancy, Positive and Negative Syndrome Scale (PANSS) response, and effect on Simpson-Angus Scale (SAS) was then developed. The empirical models describing the D(2)-PANSS and D(2)-SAS relationships were used successfully to aid dose selection for asenapine phase II and III trials. A broader use can be envisaged as a dose selection tool for new antipsychotics with D(2) antagonist properties in the treatment of schizophrenia.

[Expanding therapeutic reference ranges using dose-related reference ranges]

Evidence-based therapeutic drug monitoring (TDM), which may be successfully employed to guide drug therapy in clinical routine, supplies all the information from laboratory determination of a drug concentration in a patient's blood specimen. This value is interpreted first of all in relation to a therapeutic reference range that must be established according to the same rules that are generally accepted for clinical studies aimed to license a new drug. The drug concentration may be furthermore interpreted in reference to a dose-related reference range. Thereby a signal is created to alert for individual abnormalities such as drug/drug interactions, gene polymorphisms that give rise to slow/rapid metabolizers, altered function of the excretion organs liver and kidneys by age and/or disease, compliance problems, a missing pharmacokinetic steady state, and even signal overlay in the laboratory analysis. We return all information available and clinical pharmacological comments to physicians who send specimens to our laboratory.

Classification of orally administered drugs on the World Health Organization Model list of Essential Medicines according to the biopharmaceutics classification system

Since its inception in 1995, the biopharmaceutical classification system (BCS) has become an increasingly important tool for regulation of drug products world-wide. Until now, application of the BCS has been partially hindered by the lack of a freely available and accurate database summarising solubility and permeability characteristics of drug substances. In this report, orally administered drugs on the Model list of Essential Medicines of the World Health Organization (WHO) are assigned BCS classifications on the basis of data available in the public domain. Of the 130 orally administered drugs on the WHO list, 61 could be classified with certainty. Twenty-one (84%) of these belong to class I (highly soluble, highly permeable), 10 (17%) to class II (poorly soluble, highly permeable), 24 (39%) to class III (highly soluble, poorly permeable) and 6 (10%) to class IV (poorly soluble, poorly permeable). A further 28 drugs could be provisionally assigned, while for 41 drugs insufficient or conflicting data precluded assignment to a specific BCS class. A total of 32 class I drugs (either certain or provisional classification) were identified. These drugs can be further considered for biowaiver status (drug product approval based on dissolution tests rather than bioequivalence studies in humans).

Preanalytic aspects in postmortem toxicology

The preanalytic phase has been recognized to have a substantial role for the quality and reliability of analytical results, which very much depend on the type and quality of specimens provided. There are several unique challenges to select and collect specimens for postmortem toxicology investigation. Postmortem specimens may be numerous, and sample quality may be quite variable. An overview is given on specimens routinely collected as well as on alternative specimens that may provide additional information on the route of administration, a long term or a recent use/exposure to a drug or poison. Autolytic and putrefactive changes limit the selection and utility of specimens. Some data from case reports as well as experimental investigations on drug degradation and/or formation during putrefaction are discussed. Diffusion processes as well as postmortem degradation or formation may influence ethanol concentration in autopsy specimens. Formalin fixation of specimens or embalmment of the corpse may cause considerable changes of initial drug levels. These changes are due to alterations of the biological matrix as well as to dilution of a sample, release or degradation of the drug or poison. Most important seems a conversion of desmethyl metabolites to the parent drug. Some general requirements for postmortem sampling are given based on references about specimen collection issues, for a harmonized protocol for sampling in suspected poisonings or drug-related deaths does not exist. The advantages and disadvantages of specimen preservation are shortly discussed. Storage stability is another important issue to be considered. Instability can either derive from physical, chemical or metabolic processes. The knowledge on degradation mechanisms may enable the forensic toxicologist to target the right substance, which may be a major break down product in the investigation of highly labile compounds. Although it is impossible to eliminate all interfering factors or influences occurring during the preanalytic phase, their consideration should facilitate the assessment of sample quality and the analytical result obtained from that sample.

Age-related alteration of haloperidol-serum protein binding

Serum haloperidol levels were determined in 59 patients, 50-88-years-old, with psychosis, receiving long-term treatment with haloperidol. Although the total (bound and free form) haloperidol level in serum showed a linear correlation with daily dose, there was a larger variation in the relationship between free form and the daily dose compared with total because of inter-individual variation in the serum protein binding of haloperidol. The free fraction of haloperidol in serum increased with age. There was no difference in the ratio of total haloperidol level per daily dose between the adult and elderly groups, whereas the ratio of free haloperidol level per daily dose was significantly higher in the elderly than in the adult group. In the elderly, therefore, the therapeutic window of haloperidol should be assessed using free form level rather than total level, which is influenced by serum protein binding of the drug.

Reversible metabolism of drugs

Many drugs undergo reversible metabolism. The basis of our understanding of this process is the reversible metabolism of prednisone (PD)-prednisolone (PL). The pharmacokinetics of reversible metabolism requires the use of four area under the curve values integrated into four equations for clearance (CL). Other variables, such as linear versus non-linear disposition, can play important roles in reversible metabolism. Of recent interest is the reversible metabolism of haloperidol which consists of an interconversion process between the parent drug haloperidol (HL) and its reduced metabolite (RH). However, the interconversion of HL-RH differs from the PD-PL model in that, whereas PD and PL are both active, RH is considered to be a therapeutically inactive, possibly toxic, metabolite. This article reviews the pharmacodynamic and pharmacokinetic properties of HL and RH and the possible clinical effects that can result from this reversible metabolism.

Population pharmacokinetics of haloperidol using routine clinical pharmacokinetic data in Japanese patients

OBJECTIVE

To clarify the observed variability of haloperidol disposition in patients with psychiatric disorders.

DESIGN

Retrospective population pharmacokinetic study.

PARTICIPANTS

218 Japanese patients aged 16 to 82 years who provided 391 serum haloperidol concentrations.

METHODS

Routine clinical pharmacokinetic data gathered from patients receiving haloperidol were analysed to estimate population pharmacokinetic parameters with the nonlinear mixed effects model (NONMEM) computer program.

RESULTS

The final pharmacokinetic model was CL = 42.4 * (TBW/60)(0.655) * 0.814(AGE> or = 55) * (DOSE/200)(0.236) * 1.32(ANTIEP) and Vd = 34.4 * TBW * 0.336( AGE> or = 65), where CL is total body clearance (L/h), Vd is apparent volume of distribution (L), TBW is total bodyweight (kg), DOSE is daily dosage (microg/kg/day), ANTIEP = 1 for concomitant administration of antiepileptic drugs (phenobarbital, phenytoin or carbamazepine) and 0 otherwise, AGE > or = 55 = 1 for patient aged 55 years or over and 0 otherwise, and AGE > or = 65 = 1 for patient aged 65 years or over and 0 otherwise. Concomitant administration of haloperidol and antiepileptic drugs resulted in a 32% increase in haloperidol clearance. Patients aged 55 years or over showed an 18.6% reduction in clearance, and elderly patients aged 65 years or over showed a 66.4% reduction in apparent volume of distribution. Inclusion of terms for the concomitant administration of haloperidol and antiparkinsonian drugs (amantadine, bromocriptine, biperiden, trihexyphenidyl or mazaticol) or cytochrome P450 (CYP) 2D6 substrates (levomepromazine, perphenazine, thioridazine, amitriptyline or clomipramine) did not significantly improve the estimate of haloperidol clearance.

CONCLUSION

Application of the findings in this study to patient care may permit selection of an appropriate initial maintenance dosage to achieve target haloperidol serum concentrations, thus enabling the clinician to achieve the desired therapeutic effect.

Pharmacokinetics of haloperidol: an update

Haloperidol is commonly used in the therapy of patients with acute and chronic schizophrenia. The enzymes involved in the biotransformation of haloperidol include cytochrome P450 (CYP), carbonyl reductase and uridine diphosphoglucose glucuronosyltransferase. The greatest proportion of the intrinsic hepatic clearance of haloperidol is by glucuronidation, followed by the reduction of haloperidol to reduced haloperidol and by CYP-mediated oxidation. In studies of CYP-mediated disposition in vitro, CYP3A4 appears to be the major isoform responsible for the metabolism of haloperidol in humans. The intrinsic clearances of the back-oxidation of reduced haloperidol to the parent compound, oxidative N-dealkylation and pyridinium formation are of the same order of magnitude, suggesting that the same enzyme system is responsible for the 3 reactions. Large variation in the catalytic activity was observed in the CYP-mediated reactions, whereas there appeared to be only small variations in the glucuronidation and carbonyl reduction pathways. Haloperidol is a substrate of CYP3A4 and an inhibitor, as well as a stimulator, of CYP2D6. Reduced haloperidol is also a substrate of CYP3A4 and inhibitor of CYP2D6. Pharmacokinetic interactions occur between haloperidol and various drugs given concomitantly, for example, carbamazepine, phenytoin, phenobarbital, fluoxetine, fluvoxamine, nefazodone, venlafaxine, buspirone, alprazolam, rifampicin (rifampin), quinidine and carteolol. Overall, drug interaction studies have suggested that CYP3A4 is involved in the biotransformation of haloperidol in humans. Interactions of haloperidol with most drugs lead to only small changes in plasma haloperidol concentrations, suggesting that the interactions have little clinical significance. On the other hand, the coadministration of carbamazepine, phenytoin, phenobarbital, rifampicin or quinidine affects the pharmacokinetics of haloperidol to an extent that alterations in clinical consequences would be expected. In vivo pharmacogenetic studies have indicated that the metabolism and disposition of haloperidol may be regulated by genetically determined polymorphic CYP2D6 activity. However, these findings appear to contradict those from studies in vitro with human liver microsomes and from studies of drug interactions in vivo. Interethnic and pharmacogenetic differences in haloperidol metabolism may explain these observations.

Prediction of changes in the clinical pharmacokinetics of basic drugs on the basis of octanol-water partition coefficients

A physiologically based pharmacokinetic model for basic drugs has been established on the basis of octanol-water partition coefficients of the non-ionized, unbound drugs (Poct). The parameters for the physiological model in man were estimated from a regression equation obtained for the relationships between the Poct and the tissue-plasma partition coefficient, the hepatic intrinsic clearance (CLint,h) and the blood-to-plasma concentration ratio in rabbits. The plasma concentrations observed after intravenous administration of ten basic drugs (3.2 mg kg-1) to rabbits agreed with the levels predicted using the physiological model (r = 0.710-0.980). In man, the predicted plasma concentrations of basic drugs were in good agreement with reported values (r = 0.729-0.973), except for diazepam and pentazocine. Variations in plasma and brain-concentration profiles of clomipramine and nitrazepam in various disease states were simulated using the model. We assumed that the changes in unbound fraction of drug in serum (fp), CLint,h and the hepatic blood flow rate were from 0.25- to 4-fold that of the control and that fat volume changed by 0.2- to 5-fold. With regard to changes in fp, we predicted that the brain-plasma concentration ratio of clomipramine was 1.5- to 25-fold that of the control 24 h after intravenous administration, although the variations in the plasma concentration-time profiles were less marked. Plasma concentrations predicted for several basic drugs were in good agreement with reported values and this physiological model could be useful for predicting drug-disposition kinetics in man.

Inhibition of haloperidol reduction by non-steroidal anti-inflammatory drugs in human liver cytosol

A thorough knowledge of drug-drug interactions is crucial as the practice of multiple drug therapy escalates. In vitro studies using human liver enzymes are a valuable and non-invasive tool for predicting potential drug interactions in vivo. 1. A simple radio-TLC method was developed to monitor the formation of reduced haloperidol from haloperidol in human liver cytosol. 2. Indomethacin, known to be a potent inhibitor of 3a-hydroxysteroid dehydrogenase, was chosen as a reference for the evaluation of several arylpropionic acid derived non-steroidal anti-inflammatory drugs, ketoprofen, tiaprofenic acid, fenbufen, Ibuprofen, d-naproxen and 1-naproxen. The IC₅₀ ranged from 0.4-6.0 mM with indomethacin the most potent inhibitor of haloperidol carbonyl reductase. 3. The carbonyl reduction of haloperidol was inhibited significantly by these most commonly used non-steroidal anti-inflammatory drugs and the degree of inhibition reflected their pharmacological potency. 4. Sephadex G-100 fractionation of human liver cytosol yielded a fraction with haloperidol reductase activity at a molecular weight of about 32,000.

Effect of alosetron (a new 5-HT3 receptor antagonist) on the pharmacokinetics of haloperidol in schizophrenic patients

Alosetron is under clinical development for the treatment of schizophrenia. This study evaluated the effect of oral alosetron dosing on the pharmacokinetics of haloperidol, the latter being administered daily to 13 schizophrenic patients for 56 days. Alosetron 1 mg daily or placebo was given by random assignment for 2 weeks. After a two-week alosetron washout period (during which patients received placebo), patients received the alternate treatment for another two weeks. Serial blood samples were collected for high-performance liquid chromatography determination of plasma haloperidol, reduced haloperidol, and alosetron at selected times for 24 hours after administration of haloperidol and alosetron on study days 21 and 49. Mean pharmacokinetic parameters of haloperidol in the presence of alosetron and placebo treatments were not significantly (P > .05) different: dose-normalized Cmax (6.40 versus 5.75 ng/mL), dose-normalized Cmin (2.00 versus 1.90 ng/mL), dose-normalized AUC (85.97 versus 68.48 ng.hr/mL), and CL/f (78.23 versus 104.7 L/hr). A two-compartment model was used to assess the concentration- and time-independent pharmacokinetics of haloperidol after multiple dosing. The model confirmed that there was no change in the pharmacokinetics of haloperidol when alosetron was administered concomitantly. Mean AUC ratios of reduced haloperidol to haloperidol (0.18) in the presence of alosetron were similar to values obtained in the absence of alosetron, indicating that alosetron had no influence on the metabolism of haloperidol. Mean pharmacokinetic parameters of alosetron were similar to those in previous studies in healthy subjects.

Comparison of haloperidol and reduced haloperidol plasma levels in four different ethnic populations

1. Plasma haloperidol and reduced haloperidol concentration were measured in four ethnic populations. 2. Plasma samples were obtained under steady-state conditions and obtained 10-12 hours post bedtime dose and prior to the morning dose. 3. Haloperidol and reduced haloperidol plasma levels were assayed by radioimmunoassay and liquid chromatography. 4. A wide interpatient variability between haloperidol dose and plasma concentration was observed for each ethnic group. 5. The Chinese group differed from the other ethnic populations. 6. A nonlinear relationship was observed between haloperidol and reduced haloperidol plasma levels in each ethnic group. Further, the relationship of haloperidol to reduced haloperidol plasma levels differed for each ethnic group. These results suggest that various ethnic groups could metabolize haloperidol and reduced haloperidol differently.

Pharmacokinetics of haloperidol and reduced haloperidol in Chinese schizophrenic patients after intravenous and oral administration of haloperidol

The pharmacokinetics of haloperidol were studied in eight Chinese schizophrenic patients after intravenous administration and in six of the patients who also received oral haloperidol. After intravenous dosing, haloperidol disposition was best characterized by a three compartment model. The mean elimination half-life of 54.8 h determined by model dependent analysis was similar to the mean elimination half-life of 59.9 h determined by model independent analysis. The mean plasma clearance was 21.71/h and the mean volume of distribution during the distribution phase was 1754.3 1. After oral dosing, bioavailability of haloperidol was 35 +/- 8%, suggesting extensive first pass metabolism. Determination of reduced haloperidol concentration confirmed a previous finding of significant variability in haloperidol reductive capacity in individual patients. Comparison of area under the plasma concentration-time curve of reduced haloperidol after intravenous and oral administration of haloperidol suggests that reduction of haloperidol may only account for a small portion of first pass metabolism of haloperidol. However, conversion of reduced haloperidol back to haloperidol necessitates the monitoring of both haloperidol and reduced haloperidol concentrations in clinical practice.

Linear pharmacokinetics of haloperidol in the rat

Pharmacokinetics of haloperidol in the rat following intravenous bolus doses of 0.5, 1.0, and 2.5 mg kg-1, respectively, were investigated. It was found that haloperidol was a high extraction ratio drug with a total blood clearance averaging 83 ml min-1 kg-1. The volumes of distribution were large with a mean of 5.5 1 kg-1 (Vc), 11.11 kg-1 (V beta), and 9.61 kg-1 (Vss), respectively. The terminal half-life was 1.5 h. The disposition kinetics of haloperidol was found to be linear over the dose range studied. After constant intravenous infusions of haloperidol by different infusion rates during 12 h, steady-state levels were reached in the blood. The measured steady-state blood concentrations were consistent with those predicted by a biexponential infusion model based on the parameters obtained from the intravenous bolus study. The total blood clearance at steady-state was concentration-independent within the investigated range of 5 to 20 ng ml-1.

A pharmacodynamic model to predict the time dependent adaptation of dopaminergic activity during constant concentrations of haloperidol

The concentration-response relationship of the accumulation of brain homovanillic acid (HVA) has been studied by giving rats a shorter (12 h) and a longer (76 h) constant intravenous infusion of haloperidol, respectively, at rates aiming at different steady state blood concentrations of haloperidol of 5 to 30 ng mL-1. The observed response on brain HVA concentration vs increasing steady state blood concentration of the drug produced a bell-shaped type of curve during the 12 h infusion. When the infusion proceeded for 76 h a similar type of curve was obtained but it was shifted downwards compared with the 12 h infusion. The dopaminergic activity of the rat brain, as reflected by the HVA levels, therefore adapted to a lower activity during the prolonged exposure to haloperidol. To follow the time course of this adaptation, one steady state level of about 12 ng mL-1 was established and kept for 12, 28, 52 and 76 h. The result showed that the accumulation of brain HVA decreased over time compared with control animals given placebo. A pharmacodynamic model was set up to quantitatively describe the time-dependent adaptation of HVA accumulation in the whole rat brain during constant haloperidol administration. By fitting this model to all three sets of experimental data simultaneously, an adaptation half-time of about 38 h +/- 14 (s.d.) and a tolerance potency of about 7 ng mL-1 were obtained which could be used to calculate that, for example, at a constant blood level of 10 ng mL-1 haloperidol over 5 days the accumulation of brain HVA decreased by approximately 91% of the maximal decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Haloperidol decanoate in chronic schizophrenia: a study of 12 months with plasma levels

1. Clinical activity, extrapyramidal side-effects were evaluated in 22 schizophrenic out patients diagnosed according to DSM III and treated with haloperidol decanoate (50-300 mg i.m. monthly dose) for 12 months. 2. BPRS total scores did not show significant fluctuations showing a clinical stability of the patient population. 3. Patients with a duration of illness greater than 10 yrs (Group 2) showed significant (p less than 0.01) higher EPSE total scores compared to those with a duration of illness less than 10 yrs (Group 1). 4. A positive correlation was found between the administered dose and haloperidol plasma levels. 5. Patients from Group 2 reached the steady-state more slowly and showed a lower total L/D ratio compared to those from Group 1. 6. The pharmacokinetic approach seems desirable in order to adjust the dose and avoid schizophrenic relapses.

Comparative bioavailability of a new commercial tablet formulation and two lots of a reference formulation of haloperidol

The bioavailability of a new tablet formulation (5 mg) of haloperidol was estimated relative to two lots of a reference product. Twenty-eight healthy male volunteers completed all three phases in that they received the test (T) and the two reference formulations (R1 and R2) in a balanced three-way crossover design. Using a sensitive HPLC method, plasma concentrations of haloperidol and reduced haloperidol were monitored over a period of 96 h following administration of each formulation. Haloperidol was measurable in the plasma of all the volunteers, whereas reduced haloperidol was measurable in only 6 out of 28 volunteers following each administration. Therefore, the assessment of bioequivalence in this study is based on haloperidol data only. The maximum plasma concentration (Cmax), time to Cmax (tmax), and area under the curve up to the last measurable concentration (AUCot) or infinity (AUCo infinity) were compared by analyses of variance and found not to be significantly different across the formulations. The relative bioavailability based on T:R1 or T:R2 ratios of AUCo infinity, AUCot, and Cmax was, in each case, within the acceptable range of 100 +/- 20%. Also, the relative bioavailability of R1 compared with R2 was within 100 +/- 20% in terms of the above bioavailability parameters. Except for tmax, all other pharmacokinetic parameters showed wide intersubject variation.

Pharmacokinetics of neuroleptic drugs and the utility of plasma level monitoring

Variability in response to antipsychotic drug treatment may be caused by variable patient compliance, interactions with other drugs, pharmacokinetic variations and variations in concentration-response relationships at the receptor level. Pharmacokinetic variations may in some cases be compensated by individual dosage adjustments based on plasma drug level measurements. The interpatient variability in response to a certain time-course of drug concentrations at the receptor site could hitherto only be assessed by clinical judgement. New methods for in vivo assessment of receptor occupancy hold promise for possible measurement of parameters accounting for at least part of the interindividual variation in drug response at the receptor level. Monitoring of fluphenazine, perphenazine, thiothixene and sulpiride plasma levels by specific chemical assay methods seems to offer some guidance to individualization of drug doses. Definite therapeutic plasma level ranges have not been established for chlorpromazine and haloperidol. However, monitoring plasma levels of chlorpromazine or haloperidol might be of value when drug-induced toxicity is suspected, and as a means of controlling patient compliance.